There has bee known a bendable metal foil covered board for a flexible printed circuit comprising a film of polymide or polyester and a metal foil covered on the film. Although such a metal foil covered board has a good characteristic of repeated bending, it has no reinforcing base, which causes a large shrinkage of the board in size due to heat applied thereto. This disadvantageously limits the range of use thereof.
There has been also known a metal foil covered laminate comprising a sheet-like base of glass nonwoven fiber or paper impregnated with thermosetting resin such as epoxy resin and phenol resin and a metal foil thermally adhered to the sheet-like base. Although such a laminate has a bending characteristic if it is relatively thinner, it is not suitable for using it in a bent condition because it will be easily damaged by bending it to an extreme degree such as more than 180 degree.
There has been proposed a metal foil covered laminate comprising a sheet-like base formed of nonwoven fiber which is a blend of glass fiber and polyester fiber impregnatd with epoxy resin and a metal foil thermally adhered to the sheet-like base as disclosed in extreme degree Japanese Pat. Application Laying-Open No. 184,587/1984. However, the laminate having conventional epoxy resin included therein is not suitable for use in a bent condition. The prior art does not disclose what type of epoxy resin is used for providing a bendable laminate.
An electronic instrument has a tendency to have minimized thickness and size, which requires a printed circuit board to be contained while bent in a small space. However, there has been proposed no printed circuit board having a good bending characteristic and a minimized size shrinkage.